Gaseous hydrocarbons, which are hydrocarbons that are gaseous at mild environmental temperatures such as 20° C. and atmospheric pressure, are often transported great distances by tanker in liquid form as LNG (liquified natural gas). To keep the gas liquid, it is stored on the tanker at a low temperature such as −160° C. in highly thermally insulated tanks. At the tanker offloading destination, the LNG is offloaded to a receiving station where it is regassed (heated to turn it into a gas) and stored for later use.
Proposed prior art offloading stations include a large fixed platform extending up from the sea floor to a height above the sea surface. Such platform would contain a heating system that regassed the LNG, a pump system that pressurizes the gas, and crew quarters or other crew facilities. The regas unit or system must heat the LNG sufficiently that the gas is warm enough to avoid ice formations around noncryogenic hoses or pipes that carry the gas, and the pump system must pump the gas to a high enough pressure to inject it into a storage cavern and/or pump the gas to a shore station. A platform that is large enough to carry such gas heating and pumping systems would be expensive.
One large expense in operating such as system is the tanker daily rate, which may be about US $100,000 per day. It is therefore desirable to offload the tanker as rapidly as possible. This leads to the need for the receiving facility to be able to receive and process all LNG received so the tanker can sail away in a short period of time, and so the tanker can return soon thereafter and unload a new load of LNG. This is in addition for the need to be able to construct the receiving facility at minimum cost.